The first-order high-pass filter influences the automatic measurements of the electrocardiogram

We have studied the effects of the 0.05 Hz first-order high-pass filter (AC coupling) on the automatic measurements of the electrocardiogram (ECG). The standard 12-lead ECG of 1248 patients and the automated measurements of the AC-and DC-coupled (unfiltered) versions were compared. We found a strong, linear correlation between the QRS integral and the difference in ST-segment amplitudes, suggesting that the AC coupling alters the ST segment. The effect on the remaining part of the ECG was minimal. Medical professionals and developers of software for ECG interpretation should be aware of such high-pass filter effects, since they could be misinterpreted as pathophysiology or some pathophysiology could be masked by these effects.